1. Field of the Invention
The present invention relates to a conductive resin composition obtained by mixing conductive fibers into a thermoplastic resin and an electromagnetic wave shielding molded product using the conductive resin composition.
2. Description of the Related Art
Conductive resin compositions obtained by mixing conductive fibers into thermoplastic resins have been used in the fabrication of conductive resin molded products. Carbon-based conductive fibers have been mainly mixed in the above conductive resin compositions, and the resultant compositions have been primarily used in antistatic applications. These compositions do not have high conductivity and are not effective for electromagnetic wave shielding which has received a great deal of attention in recent years. Under these circumstances, metal-based conductive fibers are used to increase the conductivity so as to prepare compositions for electromagnetic wave shielding.
When metal-based conductive fibers (to be referred to as metal fibers hereinafter) are mixed in a thermoplastic resin, the specific gravity of the resultant composition is undesirably increased and the properties inherent to the resin are greatly degraded. Therefore, a mixing ratio of the metal fibers to the resin must be minimized. When the content of the metal fibers is decreased, the conductivity is lowered to greatly limit the application conditions. More specifically, the conductivity is lowered at high temperatures due to a difference between the thermal expansion coefficients of the resin and the metal fibers. For this reason, in practice, the content of the metal fibers is increased to prevent a decrease in conductivity and the application environments are limited. The conventional conductive resin composition and its molded product are used under such limited application environments. In addition, their properties are unstable and therefore their reliability is low.
A method is known to those skilled in the art wherein a low-melting point metal is mixed in a thermoplastic resin. The low-melting point metal has a low bonding strength with the resin. In addition, the resin is separated from the low-melting point metal in preliminary molding for color changeover in a molding machine. As a result, only the metal is scattered, thus endangering workers in the molding process.